The answer depends on what version of Office you have. You can read the
End User License Agreement that applies to your copy of Office by
starting Word, then clicking on Help | Microsoft Word Help | Contents
tab | click on the + next to "Microsoft Word Help" to expand the topic,
and select "End User License Agreement" from the list of topics. In the
EULA, there will be a section entitled "General License Grant to Install
and Use" that says how many computers (and what types of computers) you
can install your copy of Office on.